The present invention relates to a method of growing a planar-doped epitaxial layer structure of III-V compound semiconductors and more particularly to a method of controlling the carrier concentration thereof.
In a conventional planar-doped structure as reported in IEEE Transaction on Electron Devices, Vol. ED-33, No. 5, May 1986, pp. 625-632, only a selected layer of GaAs is doped with silicon (Si) as an n-type impurity element while the GaAs epitaxial layer is grown by molecular beam epitaxy (MBE). However, it is extremely difficult to define the doping position in the order of atomic layer thickness at an arbitrary depth when the epitaxial growth is resorted to the MBE technique, and thus its reproducibility is poor.
To this end, the present applicant proposed a new planar doping technique by using Atomic Layer Epitoxy (ALE) in the co-pending U.S. Pat. application filed on Mar. 28, 1988.
This new planar doping technique for producing n-type III-V compound semiconductor comprises a first step of growing a plurality of monolayers of III-V compound semiconductor molecules on a III-V compound substrate; a second step of growing a single layer of group VI element such as Selenium (Se) on the III-V monolayers so as to occupy the lattice points for group V element by means of ALE process; and a third step of growing a plurality of monolayer of III-V compound semiconductor molecules on the group VI element-doped layer by means of ALE process.
According to this method, position of the planar-doped layer can be controlled with a precise reproducibility.
On the other hand, the carrier concentration of Se-doped planar layer was controlled by the growth temperature. However, the temperature exceeds more than 550.degree. C., the carrier concentration decreases rapidly. In the same manner, when the temperature becomes less than 420.degree. C., the carrier concentration is decreased rapidly too. Accordingly, although the large value of the concentration can be achieved with a good reproducibility, it is difficult to obtain a lower carrier concentration with a good reproducibility. So long as the value of the concentration is resorted to the temperature control, wide range of the concentration cannot be obtained stably.